You know how it is.
Because I never had parents live to senior age, I find that older people either try my patience or bring me to tears of joy.
Now I visit my aged MIL (who always disliked me for taking her baby, and now has no clue who I am, so is pleasant) and my aged FIL who is and always will be darling. It’s all I can do.
That’s funny about your MIL.
My mother, in the last 2 years of her life, lost memory of her loved ones, although she continued to be pleasant and polite.
One of my brothers has a wife that Mother never cared for. But Mother was always polite to this DIL and never made her dislike obvious to my brother or to his wife, although she would sometimes make comments about her to my sisters and me in private.
My sisters and I found it amazing that, even when she no longer remembered who this DIL of hers was, Mother seemed to remember that she did not like her. She did not say anything rude, but she would make faces and did not want to be seated near this DIL.